Abrasive articles comprising abrasive particles are used to abrade and/or finish a wide variety of materials, commonly referred to as workpieces, in a wide variety of applications. These applications range from high pressure, high stock removal of metal forgings to polishing eyeglasses.
Abrasive particles, which can include grains and/or agglomerates, have a wide range of properties which provide for their application in the abrasives industry. The selection of a particular type of abrasive particle generally depends on the physical properties of the particles, the workpiece to be abraded, the surface properties desired to be achieved, the performance properties of the abrasive particles, and the economics of selecting a particular abrasive particle for a specific application.
Aluminum oxide, or alumina, is one of the most popular abrasive particles used in the production of coated abrasives, e.g., sandpaper. Alumina is used for a great many applications, such as paint sanding, metal grinding, and plastic polishing. Silicon carbide, also a popular abrasive, is generally known as a sharper mineral than alumina, and is used mainly in woodworking, paint, and glass grinding applications. Diamond and cubic boron nitride (hereafter "CBN"), commonly called "superabrasives," are especially desirous in abrading very hard workpieces such as hardened steel, ceramic, cast iron, and stone. Diamond is typically the preferred superabrasive for non-ferrous materials, while CBN is typically the preferred superabrasive for ferrous materials like hardened steel. However, superabrasives such as diamond and CBN can cost up to 1000 times more than conventional abrasive particles, i.e., aluminum oxide, silicon carbide. Therefore, it is desirable to utilize the superabrasives their full extent.
As noted above, abrasive particles can be in the form of single grains or agglomerates. Abrasive agglomerates are composite particles of a plurality of single abrasive grains bonded together by a binder. During abrading, the agglomerates typically erode or break down and expel used single abrasive grains to expose new abrasive grains. Agglomerates can be used in abrasive products such as coated abrasives, non-woven abrasives, and abrasive wheels and provide a long useful life and efficient use of the abrasive particles.
U.S. Pat. No. 2,001,911 discloses an abrasive article having a flexible backing and numerous small portions of bonded abrasive material which are adhered to the backing by a layer of flexible and resilient intermediate material. The bonded abrasive material consists of a plurality of abrasive blocks mounted on the backing and separated from each other on their sides by narrow fissures.
U.S. Pat. No. 2,194,472 discloses an abrasive article comprising a backing, which can be flexible, and a coating of abrasive aggregates which are porous, angular, and unflattened and which comprise a plurality of single abrasive grains bound together by a bond system. Preparation of an abrasive article can entail screening the aggregates to provide aggregate particles of a reasonably uniform size.
U.S. Pat. No. 3,986,847 discloses an abrasive article such as a grinding wheel having an abrasive section comprising an abrasive phase and a vitreous bond. The abrasive phase comprises either CBN alone or in combination with a second abrasive grain having a coefficient of thermal expansion substantially the same as the coefficient of thermal expansion of CBN. The vitreous bond is a glassy bond having a coefficient of thermal expansion substantially the same as the coefficient of thermal expansion of CBN.
U.S. Pat. No. 4,256,467 discloses a flexible abrasive article comprising a flexible non-electrically conductive mesh material and a layer of electro-deposited metal, which contains diamond abrasive material embedded therein, adhered directly to and extending through the mesh material so that the mesh material is embedded in the metal layer.
U.S. Pat. No. 4,393,021 discloses a method for the manufacture of granular grit particles in which the individual grits are mixed with a binding medium and a filler to form a pasty mass. The mass can be extruded, heated to harden the mass, and then the hardened product can be broken into granular grit particles, each including several individual grits.
U.S. Pat. No. 4,799,939 discloses an abrasive article comprising erodible agglomerates containing individual abrasive grains disposed in an erodible matrix comprising hollow bodies and a binder. The individual abrasive grains can include aluminum oxide, carbides such as silicon carbide, nitrides such as CBN, diamond, and flint. Although the binder is preferably a synthetic organic binder, natural organic binders and inorganic binders can also be used. The agglomerates are typically irregular in shape but can be formed into spheres, spheroids, ellipsoids, pellets, rods, or other conventional shapes.
U.S. Pat. No. 4,871,376 discloses a coated abrasive comprising a substrate backing, an abrasive material, and a bond system comprising a resinous adhesive, inorganic filler, and a coupling agent. The coupling agent can be selected from the group consisting of silane, titanate, and zirconaluminate coupling agents.
U.S. Pat. No. 5,039,311 discloses an abrasive article comprising an erodible abrasive granule comprising a plurality of first abrasive grains bonded together by a first binder to form an erodible base agglomerate, the base agglomerate at least partially coated with second abrasive grains bonded to the periphery of the base agglomerate by a second binder. The first and second binder, which can be the same or different, can be organic or inorganic and can contain additives such as fillers, grinding aids, plasticizers, wetting agents, and coupling agents. The first and second abrasive grains can be the same or different and can include aluminum oxide, silicon carbide, diamond, flint, CBN, silicon nitride, and combinations thereof. The base agglomerate is typically irregular in shape but can be formed into spheres, spheroids, ellipsoids, pellets, rods, or other conventional forms.
U.S. Pat. No. 5,152,917 discloses a coated abrasive article comprising a backing have at least one major surface and abrasive composites on the at least one major surface. The abrasive composites comprise a plurality of abrasive grains dispersed in a binder, which may also serve to bond the abrasive composites to the backing, and have a predetermined shape, for example, pyramidal.
U.S. Pat. No. 5,210, 916 discloses an abrasive particle prepared by introducing a boehmite sol into a mold in which the mold cavities are of a specified shape, removing a sufficient portion of the liquid from the sol to form a precursor of the abrasive particle, removing the precursor from the mold, calcining the removed precursor, and sintering the calcined precursor to form the abrasive particle. The mold cavity has a specified three-dimensional shape and can be a triangle, circle, rectangle, square, or inverse pyramidal, frusto-pyramidal, truncated spherical, truncated spheroidal, conical, and frusto-conical.
U.S. Pat. No. 5,314,513 discloses an abrasive article having a flexible substrate, at least one layer of abrasive grains bonded to the front side of the substrate by a make coat and optionally one or more additional coats, wherein at least one of the coats comprises a maleimide binder.
U.S. Pat. No. 5,318,604 discloses an abrasive article comprising abrasive elements dispersed in a binder matrix. The abrasive elements comprise individual particles of abrasive material, substantially all of which are partially embedded in a metal binder.
German Patent No. OS 2941298-A1, published Apr. 23, 1981, teaches coated abrasive articles comprising abrasive conglomerates, which have a rugged and irregular surface, prepared by intensively mixing abrasive mineral grains with glass frit and binder; processing the mixture; pressing, drying, and sintering the material; and then crushing the material to form the conglomerate.
U.S. Ser. No. 08/085,638 discloses precisely shaped particles comprising an organic-based binder and methods for making such particles. The organic-based binder may contain a plurality of abrasive grits dispersed therein.
Although abrasive articles are generally selected based on their physical properties and the desire to maximize abrading and extend the useful life of the abrasive article, particular considerations arise when the industry desires an abrasive article having a long life which can abrade hard materials, such as camshafts and crankshafts, for example, in a camshaft belt grinder as disclosed in U.S. Pat. No. 4,833,834, while conforming to design tolerances including providing a precision ground workpiece.